Rehabilitation of District Heating Networks

District heating and combined heat and power systems are becoming an attractive way of reducing greenhouse gas emissions. This has resulted in renewed interest in such systems used to provide electricity and heat to cities, and Universities, for example. There are many district heating systems in the United Kingdom, including the cities of London, Newcastle, Nottingham and Sheffield, among others. These systems take the form of a central boiler supplying heat over a large area such as a housing estate. The distribution of hot water is by preinsulated pipelines, with the majority manufactured in steel. Primary pipelines carry superheated water from the boiler to substations where the temperature is modulated depending on demand. Secondary pipelines transport water to users and constitute the bulk of pipelines in a network. Operating temperatures of secondary pipelines can be up to 90°C but are typically at less than 80°C. Poor installation practice in the past often means that pipelines are prematurely at the end of their lives, and require constant maintenance. Clearly the maintenance costs of such a system are very large, as the installations are in a congested urban environment. The repair costs are high due to the reinstatement costs for road, footpaths, and buildings. Such high costs can result in decommissioning the district heating network, installing individual boilers and bearing the resultant short term costs. In these circumstances there is a clear market for a rehabilitation system. This paper describes such a system, manufactured from crosslinkable polyethylene. The general properties of PEX are reviewed and key properties for this application are selected and the requirements stated. The performance of the product against specified criteria is described in depth. The results of yard trials are reviewed and a case study of a field trial in Byker, Newcastle-upon-Tyne is given, demonstrating that the SPEX system provides the means to economically repair leaking pipework by a novel relining technique.